This invention relates to a process for recovering at least one metal, e.g., gold, silver, the platinum group metals and the like, from an ore containing reducible manganese and the metal. The invention also relates to a process for recovering at least one metal, e.g., as noted above, from an ore containing metal sulfides and the metal to be recovered. In particular, the invention relates to a process which involves processing a metal-containing ore so as to facilitate the recovery of the metal from the ore.
Reducible manganese-containing ores quite often contain metal values which are difficult to recover because of the "locking" nature of the manganese in the ore. For example, the occurrence of manganese-locked silver ores has long been a problem for ore processors. Conventional smelting can treat small, limited quantities of manganese-locked silver ores when processing conventional ores. The manganese must be properly slagged to prevent attack of the crucibles. This consumes silica, increases energy required, and contributes to metal loss in the slag. Manganese-locked silver ores may be leached with sodium cyanide to recover silver, but such recovery is often limited by the manganese content. Manganese in such ores "locks" the silver in the ore by, for example, blocking access by the sodium cyanide solution to the silver-bearing or silver minerals.
Metal sulfide-containing ores often contain metal values, such as gold, silver, the platinum group metals and the like, which are difficult to recover because of the "locking" nature of the metal sulfide in the ore. For example, the occurrence of insoluble metal sulfide-locked gold ores has long been a problem for ore processors. In addition, electrum-containing ores are also difficult to process for the recovery of precious metal values.
Use of sodium cyanide to remove silver from manganese-locked silver ores or to remove gold from such gold metal sulfide-containing ores is usually uneconomical. Moreover, stringent air pollution control regulations and low metal prices have forced smelters to shut down or select ores from which metal values can be recovered relatively easily. Ores which include "locking" manganese (e.g., containing about 0.5% to about 35% by weight of manganese) are often considered marginal and may not be processed.
Commonly assigned U.S. patent applications Ser. Nos. 858,056 now U.S. Pat. No. 4,752,332 and 858,369, now U.S. Pat. No. 4,740,243 filed Apr. 30, 1986, disclose processes for the recovery of various metal values, e.g., silver, gold, and the platinum group metals, involving the use of reducible manganese components. These applications also include a more detailed discussion of certain prior art references. Also, commonly assigned U.S. patent application Ser. No. 931246, filed Nov. 17, 1986, discloses a process to reduce the sulfur content of coal and petroleum. All of these applications are incorporated in their entireties by reference herein. There continues to be a need for improved processing to recover metal values, in particular from reducible manganese-containing ores and metal sulfide ores.